1. Field of the Invention
The present invention relates to a camera or image pick-up device and, more particularly, is directed to improvements in a color television camera.
2. Description of the Prior Art
In a color television camera 1 according to the prior art, as disclosed in U.S. Pat. No. 4,427,996, and as illustrated in FIGS. 1A and 1B hereof, an image of a desired camera subject is formed on a light reception surface of a solid-state pick-up element 4 by a lens 3 through a variable stop or iris.
The pick-up element 4 has complementary color filters on its light reception surface and produces an output signal corresponding to each picture element of the image which is supplied to a sample and hold circuit 5 at the timing of the raster scanning. A detector 6 receives the output or camera signal from the sample and hold circuit 5 and detects the amount of incident light impinging on the solid-state pick-up element 4 on the basis of the level of the camera signal. A comparator 7 compares the output of the detector 6 with a reference voltage from a source 8 and provides a comparison result which is applied to the stop or iris 2 for controlling the latter.
By the foregoing arrangement, the amount of the light incident on the solid-state pick-up element 4 is controlled to be equal to or less than a predetermined value so that a camera signal produced from the sample and hold circuit 5 is made to have a predetermined signal level.
Further, as is shown, a variable gain amplifier 10 receives the camera signal from the sample and hold circuit 5 and supplies a corresponding output signal to a detector 11 which detects the level of such output signal. A comparator 12 compares the output of the detector 11 with a reference voltage from a source 13 and the resulting comparison output variably controls a gain of the variable gain amplifier 10. By the foregoing arrangement, the gain of the variable gain amplifier 10 is controlled to be increased only when the amount of light is insufficient, for example, due to a dark camera subject, even when the stop 2 is fully opened. In other words, the variable stop 2 is controlled in preference to the variable gain amplifier 10, with the gain of the variable gain amplifier 10 being controlled in a range where correction cannot be achieved by the stop 2 alone, whereby a camera signal S.sub.s with a predetermined signal level is maintained.
Furthermore, as shown, a low-pass filter 15 receives the camera signal S.sub.s from the variable gain amplifier 10 and extracts therefrom a luminance signal S.sub.Y. A detector 16 receives a relatively high frequency component of the luminance signal S.sub.Y from the filter 15 through a band-pass filter 17 and provides an envelope detection output which is supplied to an analog-to-digital converter 18, and the resulting digital signal from converter 18 is supplied to a control circuit 19. The control circuit 19 provides a control signal to the lens 3 which is based on the level of the envelope detection output from detector 16 so that the focus of the lens 3 is controlled to maintain a focused state of the central portion of the projected image on the pickup element 4.
A color separation circuit 20 is also shown to receive the camera signal S.sub.s from the variable gain amplifier 10 and converts the camera signal S.sub.s into a luminance signal S.sub.YC, a composite signal R+G of red and green and a composite signal B+G of blue and green. A matrix circuit 21 converts the luminance signal S.sub.YC and the composite signals R+G and B+G into red, green and blue color signals R, G and B, respectively, and then outputs such color signal R, G and B to integrators 22, 23 and 24, respectively, and to a white balance adjustment circuit 25.
A control circuit 27 selectively receives the output signals of the integrators 22, 23 and 24 through a selector 28 and an analog-to-digital converter 29 and detects the signal levels of the color signals R, G and B on the basis of their respective integrated values. In response to such detected levels of the color signals R, G and B, the control circuit 27 generates a control signal which is supplied to the white balance adjustment circuit 25 through a digital-to-analog converter 30, so that the degrees of amplification of the red and blue color signals R and B are variably controlled for maintaining a predetermined ratio of the signal levels of the color signals R, G and B relative to each other. In that way, color signals of predetermined white balance are obtained from the white balance adjustment circuit 25, and are supplied to an encoder 34 through a gamma correction circuit 33 for the color signals.
On the other hand, a gamma correction circuit 35 receives the luminance signal S.sub.Y from the low-pass filter 15 and the resulting gamma corrected luminance signal is also supplied to the encoder 34. In the encoder 34, the color signals and the luminance signal are converted into respective color difference signals which are modulated into chroma signals, and the latter are superimposed on the luminance signal so as to provide a video signal S.sub.V.
However, in the above-described known video camera, separate control circuits are provided for control of the stop 2, the gain of the variable gain amplifier 10, the focus of the lens 3 and the white balance adjustment circuit 25. As a result, the construction of the video camera is undesirably complicated. Even the control circuits for the stop 2 and the variable gain amplifier 10 are composed of respective detectors 6 and 11, reference voltage sources 8 and 13 and comparators 7 and 12, so as to undesirably complicate the structure.
Further, it would be desirable to provide this kind of video camera with modes or functions characteristic of a single lens reflex camera, such as, a shutter preference mode and a stop preference mode in addition to an automatic adjustment mode, so that the freedom of use of the camera can be enhanced.